51,820 research outputs found
Observation of quantum spin noise in a 1D light-atoms quantum interface
We observe collective quantum spin states of an ensemble of atoms in a
one-dimensional light-atom interface. Strings of hundreds of cesium atoms
trapped in the evanescent fiel of a tapered nanofiber are prepared in a
coherent spin state, a superposition of the two clock states. A weak quantum
nondemolition measurement of one projection of the collective spin is performed
using a detuned probe dispersively coupled to the collective atomic observable,
followed by a strong destructive measurement of the same spin projection. For
the coherent spin state we achieve the value of the quantum projection noise 40
dB above the detection noise, well above the 3 dB required for reconstruction
of the negative Wigner function of nonclassical states. We analyze the effects
of strong spatial inhomogeneity inherent to atoms trapped and probed by the
evanescent waves. We furthermore study temporal dynamics of quantum
fluctuations relevant for measurement-induced spin squeezing and assess the
impact of thermal atomic motion. This work paves the road towards observation
of spin squeezed and entangled states and many-body interactions in 1D spin
ensembles
Naked Exclusion: Towards a Behavioral Approach to Exclusive Dealing
We report experimental results on exclusive dealing inspired by the literature on "naked exclusion". Our key findings are: First, exclusion of a more efficient entrant is a widespread phenomenon in lab markets. Second, allowing incumbents to discriminate between buyers increases exclusion rates compared to the non-discriminatory case only when payments to buyers can be offered sequentially and secretly. Third, allowing discrimination does not lead to significant decreases in costs of exclusion. Accounting for the observation that buyers are more likely to accept an exclusive deal the higher is the payment, substantially improves the fit between theoretical predictions and observed behavior.exclusive dealing;entry deterrence;foreclosure;contracts;externalities;coordination;experiments
Contact tracing and epidemics control in social networks
A generalization of the standard susceptible-infectious-removed (SIR)
stochastic model for epidemics in sparse random networks is introduced which
incorporates contact tracing in addition to random screening. We propose a
deterministic mean-field description which yields quantitative agreement with
stochastic simulations on random graphs. We also analyze the role of contact
tracing in epidemics control in small-world networks and show that its
effectiveness grows as the rewiring probability is reduced.Comment: 4 pages, 4 figures, submitted to PR
Semiclassical universality of parametric spectral correlations
We consider quantum systems with a chaotic classical limit that depend on an
external parameter, and study correlations between the spectra at different
parameter values. In particular, we consider the parametric spectral form
factor which depends on a scaled parameter difference . For
parameter variations that do not change the symmetry of the system we show by
using semiclassical periodic orbit expansions that the small expansion
of the form factor agrees with Random Matrix Theory for systems with and
without time reversal symmetry.Comment: 18 pages, no figure
Flat Histogram Method of Wang-Landau and N-fold Way
We present a method for estimating the density of states of a classical
statistical model. The algorithm successfully combines the Wang-Landau flat
histogram method with the N-fold way in order to improve efficiency of the
original single spin flip version. We test our implementation of the
Wang-Landau method with the two-dimensional nearest neighbor Ising model for
which we determine the tunneling time and the density of states. Furthermore,
we show that our new algorithm performs correctly at right edges of an energy
interval over which the density of states is computed. This removes a
disadvantage of the original single spin flip Wang-Landau method where results
showed systematically higher errors in the density of states at right
boundaries. We compare our data with the detailed numerical tests presented in
a study by Wang and Swendsen where the original Wang-Landau method was tested
against various other methods. Finally, we apply our method to a thin Ising
film of size with antisymmetric surface fields. With the
density of states obtained from the simulations we calculate canonical averages
related to the energy such as internal energy, Gibbs free energy and entropy,
but we also sample microcanonical averages during simulations in order to
determine canonical averages of the susceptibility, the order parameter and its
fourth order cumulant. We compare our results with simulational data obtained
from a conventional MC algorithm.Comment: Latex, 19 pages, 12 encapsulated Postscript figure
Zoo-FISH in the European mole (Talpa europaea) detects all ancestral Boreo-Eutherian human homologous chromosome associations
Zoo-FISH with human whole-chromosome paint probes delineated syntenic association of human homologous chromosome segments 3-21, 14-15, 16-19, 4-8, 7-16 and 12-22 (twice) in the European mole (Talpa europaea, Talpidae, Eulipotyphla, Mammalia). These segment associations represent shared ancestral Boreo-Eutherian traits, half of which were previously not described for Eulipotyphla. The karyotype of the European mole acquired a minimum of 19 translocations and six inversions compared to the presumed Boreo-Eutherian ancestor. Copyright (c) 2006 S. Karger AG, Basel
Voltage-flux-characteristics of asymmetric dc SQUIDs
We present a detailed analysis of voltage-flux V(Phi)-characteristics for
asymmetric dc SQUIDs with various kinds of asymmetries. For finite asymmetry
alpha_I in the critical currents of the two Josephson junctions, the minima in
the V(Phi)-characteristics for bias currents of opposite polarity are shifted
along the flux axis by Delta_Phi = (alpha_I)*(beta_L) relative to each other;
beta_L is the screening parameter. This simple relation allows the
determination of alpha_I in our experiments on YBa_2Cu_3O_(7-x} dc SQUIDs and
comparison with theory. Extensive numerical simulations within a wide range of
beta_L and noise parameter Gamma reveal a systematic dependence of the transfer
function V_Phi on alpha_I and alpha_R (junction resistance asymmetry). As for
the symmetric dc SQUID, V_Phi factorizes into
g(Gamma*beta_L)*f(alpha_I,beta_L), where now f also depends on alpha_I. For
\beta_L below five we find mostly a decrease of V_Phi with increasing alpha_I,
which however can only partially account for the frequently observed
discrepancy in V_Phi between theory and experiment for high-T_c dc SQUIDs.Comment: 4 pages, 7 figures, Applied Superconductivity Conference 2000, to be
published in IEEE Trans. Appl. Supercon
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